Page 178 - Engineering drawing from first principles using AutoCAD

Chapter ~

Fastenings

This chapter introduces commonly used fastenings which are necessary for assembly
drawings. It is possible with CAD to store frequently used details in your own data bank,
then recall and reposition items, as required.
At the end of the chapter you will be able to draw accurately:

• Nuts, bolts, studs and washers from standard dimensions.
• Understand the terminology and conventions relating to nuts and bolts.
• Draw fastenings on sectional views and assemblies.
• Draw isometric views of nuts and bolts.

Nuts and bolts

These exercises show accurate projections of nuts and bolts drawn from first principles
and using standard information. Parts of these drawings can be used in other assemblies.
They can, if desired, also be stored in block form in your own database to build a library of
regularly used components to be used on assembly drawings.

ISO metric precision hexagon bolts, screws and nuts are covered by BS 3692 and ISO 272.
The Standard also includes washer details. Tables of dimensions are listed relating to the
thread size. An M36 nut fits an M36 bolt and the 36mm dimension is the outside
diameter of the bolt. A large bolt of this nature would be used in structural steelwork
assemblies and is an ideal size for this example. The dimensions are as follows (Fig. 8.1):
nominal thread size diameter 36
minor diameter of thread 31
width across corners (A/C) 62.5
width across flats (A/F) 55
height of bolt head 23
thickness of normal nut 29
thickness of thin nut (locknut) 14
washer outside diameter 66
washer thickness 5
The construction sequence is as follows. Choose an A4 sheet size in landscape style and
draw a centre line across the sheet where Y=100, then add vertical centre lines with X=
50, X = 140 and X = 230. These are the vertical centre lines of the three stages. Draw stage
1, copy it onto the centre line of stage 2, copy stage 2 onto the centre line of stage 3, line in
the relevant parts and delete unwanted construction lines.

It is always vital to use the SNAPfeature whenever possible to maintain the accuracy of
draughting from datum positions, so that MOVE, MIRROR, COPY, and ROTATE can be
used with complete accuracy. Select Polygon in the Draw menu and the command line
reads

Command: _polygon Number of sides <4>:
Type 6 and press <Enter>. The command line now reads Edge/ <Cen tre of Polygon>: